Search form

Meditations on Trusted Computing

By Fred von Lohmann

May 24, 2004

May 2004

In 1641, in his Meditations on First Philosophy, mathematician and
philosopher Rene Descartes asked how it is that we can trust our senses.
What if, he asked, everything we experience is actually part of a delusion
created by an omnipotent demon bent on deceiving us?

It turns out that a similar question has been weighing on the minds of
Microsoft, Intel, and a number of other computer companies. How do you know
that your computer is actually what it seems? After all, hackers could have
broken into your computer and replaced the software on it with software
that imitates, in every particular, the software that was on your computer
before. To you, things would appear unchanged. But now your computer is
under the hacker's control, logging your every keystroke, copying your most
sensitive information, and sending it out over your Internet connection.

This points to another nagging epistemic doubt-how can any software on your
computer trust any other software running on your computer? For example,
when you run an anti-virus program, how can it be sure that the operating
system hasn't been subverted somehow? After all, software installed by the
hackers could intercept any warnings before they were output to your
display, replacing them with screens announcing "no problems detected."

In short, how can you be sure that everything you experience on your
computer is not part of a delusion created by hackers bent on deceiving
you?

These are not idle questions. Today, computer users are increasingly
besieged by malicious, hard-to-detect software designed to subvert
computers-viruses, Trojan horses, worms, and spyware, to name just a few.
This specter haunts not only individuals, but also a wide variety of
companies, including health care providers, movie studios, intelligence
agencies, and others who routinely entrust valuable or sensitive
information to computers.

Enter the Trusted Computing Group, comprised of Microsoft, Intel, AMD, and
several other large computer technology companies. The TCG companies are
working on technology that will let you trust that your computer is what it
appears to be.

Trusted computing: What is it?

First, you'll have to buy a new computer (did you think for a moment that a
plan hatched by the world's largest software, chip and computer companies
could start any other way?) that will include a special chip containing
cryptographic hardware and keys.

You can choose to ignore the new chip, and your computer will behave just
like the one you have now. You are free to install any operating system you
like, and any software. The chip remains dormant until you decide to take
advantage of it.

If you elect to activate the "trusted computing" features made possible by
the chip, and if your operating system has been updated to take advantage
of it, then your computer is "virtually" split in two, divided into
"untrusted" and "trusted" sides. Both "sides" share the same CPU, the same
hard drive, the same keyboard, and the same display, but the trusted side
has an additional, very special property-it cannot be subverted by other
software running on your machine. In other words, on the trusted side of
your computer, you can run software with a high level of confidence that
the software is what you think it is.

How? Well, the story depends on a great deal of sophisticated cryptography.
When the trusted side of your computer saves data to the hard drive or to
memory on behalf of a particular trusted software application, it does so
in a secure, encrypted format. This encrypted data can only be read by that
software application, running on the trusted side of your computer.

Malignant software that may be running on your computer (whether on the
trusted or untrusted side) will not be able to read the encrypted data that
belongs to another trusted application. In addition, the trusted side has a
secure, encrypted channel to your keyboard and display, so malignant
software cannot intercept data or interpose itself between you and the
trusted application.

All of this allows you to trust the integrity of the software that is
running on the trusted side, and that data saved by this software will not
be accessible to subverted software that may be running on the untrusted
side. (You are still vulnerable if a hacker has access to your hardware,
however, as the security can be breached by hardware-based attacks.)

So far, so good.

Trusting computing: Troubling implications.

Trusted computing, however, does more than allow you to trust your own
computer; it also aims to enable *others* to trust your computer. The key
to this capability is in a feature called "remote attestation." This allows
another person to ask the software running on the trusted side of your
computer to identify itself. Because the answer comes from the tamper-
resistant hardware on the motherboard of your computer, the "attestation"
is relatively reliable. This feature certainly has some desirable uses (for
employees logging into corporate networks from offsite locations, for
example).

But there is a dark side. If others are able to verify that particular
software is running on the trusted side of your computer, then some may
refuse to communicate with you at all *unless* you are running their
software. In other words, companies may begin demanding that you install
and run the software *of their choice* on the trusted side of your
computer. This would effectively give them control over a portion of your
computer. You would be free to refuse, but then you would not be able to do
business with them.

In a competitive market, this might not be a problem, as vendors would
avoid anything that might alienate customers. In a market where competition
is compromised, however, trusted computing can dramatically increase the
power of a monopolist or cartel to impose "take it or leave it" terms on
the public, by giving them the capability to insist on a relatively
unassailable beachhead inside your computer.

For example, imagine that Hollywood movie studios decide to release their
movies in formats that can only be played by certain trusted media player
software. "Remote attestation" would be used to verify that the media
player software was, in fact, running on the trusted side of your computer
and that it had not been tampered with. This would give the movie studios
unprecedented control over how your computer interacts with their movies.
Your continued ability to make copies, take excerpts, fast-forward and mute
would all be entirely within Hollywood's control, and part of your computer
would now answer to Hollywood, rather than to you.

The implications, however, reach far beyond "digital rights management"
schemes pushed by entertainment companies. Other industries may also
eagerly embrace the idea that they can demand a beachhead inside your
computer as a condition of doing business with you. For example, the
dominant vendor for a particular software application (like Microsoft Word
for word processing) could modify a future trusted version to prevent you
from migrating your documents to a competing application.

As with many technologies, trusted computing has uses both for good and for
ill, and thus should be viewed with a critical eye, lest the users end up,
in Descartes words, "as the captive, who, perchance, was enjoying in his
dreams an imaginary liberty, when he begins to suspect that it is but a
vision, dreads awakening, and conspires with the agreeable illusions that
the deception may be prolonged."

The leading nonprofit defending digital privacy, free speech, and innovation.